Hi, I wan't to make a drive circuit for LXHL-LW3C
datasheet here: https://www1.elfa.se/data1/wwwroot/webroot/Z_DATA/07511149.pdf

I'm going to use 12v power supply. Can I use LM317T from my previous project as current control chip? If so can you help me to calculate the right resistor value.

Thanks.

 

Here are specs:

Luxeon III Star LED - White Lambertian, 65 lm @ 700mA

LXHL-LW3C Specifications:
Lumens @ 700mA: 65 lm
Max Continuous Current: 1000 mA
Forward Voltage : 3.9 Vf
Dominant Wavelength: 5500 K
LED Type: Star
Radiation Pattern: Lambertian
Weight: 5.5g

I see commercial power supplies are rated for 700mA of power for 3W LED like I have and 350mA for 1W LED.

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My power supply: 12V Here is how I calculated the resistor for LM317T 1.5Amps IC:

(12v-3.9v)/0.700mA=11.571/0.700=16.53Ohms

Are my calculations correct??? because this calculator here:
http://www.reuk.co.uk/LM317-Current-Calculator.htm

Shows me that I need 1.8Ohms 0.88W resistor

 

Your calculations are wrong.

The website's calculations are based upon a typical Vref of 1.25v. Yours may be as low as 1.2, or as high as 1.3. You will need to measure it to make certain, by connecting a 100 Ohm resistor between the OUT and ADJ terminals, and connect 3v to 30v between the IN and ADJ terminals. Measure Vref between then OUT and ADJ terminals using an accurate DMM (digital multimeter).

You will need a heatsink for both the LED, and for the LM317T.

 

Look at page 18 of this:

http://www.national.com/ds/LM/LM117.pdf

The current through the load will be 1.25V/R1.

 

Some have found simple ways to build regulators. See the website
Instructables. I can not vouch for their accuracy or quality.

 

Some have found simple ways to build regulators. See the website
Instructables. I can not vouch for their accuracy or quality.

Thanks, I now changed my LED to 1W 350mA version, it suppose to give me 90% CRI rating versus 70% for "cold white" versions.

I'll measure my Vref of voltage and post it.

BTW anyone knows how to know Luxeon LED model? My LED has no writings etc.

 

Thanks, I now changed my LED to 1W 350mA version, it suppose to give me 90% CRI rating versus 70% for "cold white" versions.

I'll measure my Vref of voltage and post it.

BTW anyone knows how to know Luxeon LED model? My LED has no writings etc.

Do you have a closeup pic of both sides?
Maybe it's a fraud!